1. Field of the Invention
This invention relates to World Wide Web (WWW) technology, and more particularly, to a method and system for implementing real-time interactivity across a shared multiple-participant three-dimensional (3D) virtual-reality environment on the WWW, with the purpose of allowing a plurality of users (participants) to participate in a 3D virtual-reality world where the participants can share information and interact with each other substantially in real time.
2. Description of Related Art
Virtual reality is a computer-generated simulation of a 3D scene that a user can experience and manipulate as if it were physically real. A 3D virtual-reality environment can be, for example, a chat room, a campus, a playground, a conference room, and so on, where users can experience the virtual-reality effect through a browser program. On the Internet, a multiple-participant 3D virtual-reality environment allows a number of users at different locations to browse information and interact with the other users participating in the same 3D virtual-reality world. Inside such an environment, each participant is represented by a 3D icon, commonly referred to as an avatar, that depicts the participant's virtual-reality identity in the environment. Participating in the same virtual-reality environment, all the participants from the distributed locations can see the same scene and hear the same sound provided by the 3D virtual-reality world.
In the design of a multiple-participant 3D virtual-reality environment, it is desired to maintain spatial consistency and time coherency among the various participants. Due to the intrinsic latency in network communications, however, time coherency is nearly unattainable. Spatial consistency, on the other hand, can be attained through the use of appropriate communication protocols that can send updated data in real time to each of the participants.
On the Internet, the WWW is based on a client/server architecture under which each WWW server serves up information to each client on a request-and-response basis, i.e., the connection between the client and the server is established only when the client issues a request to the server, and after the requested information has been served, the connection is immediately broken. The request-and-response operation can help reduce network traffic. In the use of a multiple-participant system, however, the request-and-response operation leads to three drawbacks: lack of server-to-client call-back capability, lack of client information recording capability and excessive network loading.
The drawback of lack of server-to-client call-back capability arises due to the fact that the connection between client and server is established only when the client issues a request to the server and is immediately broken after the requested information has been served. Due to this drawback, it is impossible for one user to send a message to any of the other users participating in the same 3D virtual-reality world. Moreover, after the re- quested information has been served, the server will record no information about the client who has just requested information from the 3D virtual-reality world.
One solution to provide server-to-client call-back and client information recording capabilities is disclosed in "MOLTIP-UID and R-HTTP Specification" by Chin, Chee-Kai, which is available online at: EQU www.ontc.ncb.gov.sg/staff/cheekai/htm/moltip-techspe.html
Chin's method utilizes a unique user identification number, named as a MOLTIP-UID number, for each client site. The MOLTIP-UID number consists of the following pieces of data: machine type (M), operating system (O), login usemame (L), timestamp (T), process ID (I), and listening port (L). When the link between the client site and the WWW server is established, the client site will send a MOLTIP-UID number to the WWW server. For the WWW server, the Chin's method utilizes a modified HTTP protocol, called Retum-HTTP (R-HTTP), which is capable of registering related identification information about each client site connected to the WWW server and sending information back to the connected client site based on the registered identification information.
One drawback to the Chin's method, however, is that it requires a modification to the existing HTTP protocol, which would make the implementation inconvenient to carry out. There exists, therefore, a new method which requires no modification to the existing HTTP protocol on the WWW server.